Electric discharge tube



Jan. 16, 1951 A. J. W.,M. VAN OVERBEEK 2,538,714

ELECTRIC DISCHARGE TUBE Filed Feb. 17, 1949 INVENTOR. AMP/AMA) Jul/VI. V/W OI/[ABffk L U yL AGf/l/T Patented Jan. 16, 1951 ELECTRIC DISCHARGE TUBE Adrianus Johannes Wilhelmus Marie van Overbeek, Eindhoven,

Netherlands,

assignor to Hartford National Bank and Trust Company, Hartford, Conn, as trustee Application February 17, 1949. Serial No. 76,885-

' In the Netherlands April 14, 1948 The invention relates to an electric discharge tube in which a stream of electrons is formed into a beam and directed to an electron mirror functioning, in addition, as a deflection member.

Electric discharge tubes are known in which the stream of electrons emitted by a cathode is concentrated into a beam which is directed to an electrode system, a so-called electron mirror, by which the beam is reflected through a large angle. In such tubes use is frequently made of an electrode system which produces a definite deflection of the beam before reaching the electron mirror. Furthermore it is known to apply, in addition the deflection voltages to the electrodes forming the electron mirror. In this case the mirror serves at the same time as a deflection member. The constructions hitherto known of such deflecting electron mirrors primarily comprise two or more plate-shaped electrodes arranged substantially in one plane, which is sometimes curved, to which the deflection voltages are fed. In order to ensure a uniform deflection effect of the mirror at various points of its surface, the electrodes are sometimes connected in the tube comprising the mirror, through a resistance, of which the surface forms part of the electron mirror.

This system has the disadvantage that at high frequencies the deflection no longer occurs in the manner determined by the voltage division of the resistance, since at high frequencies the potential division is primarily determined by the electrostatic displacement and no longer by the galvanic currents through the resistance layer. At high frequencies, consequently, the function of the resistance is at least partly taken over by the dielectric between the electrodes.

At these high frequencies it is consequently not readily possible to influence the shape of the refleeting fleld by the proportioning of the resistance layer, so that sometimes the electrodes proper must be given complicated shapes by which the manufacture is rendered diificult. For example, the electrodes must be subdivided.

It has furthermore been suggested to construct a deflecting electron mirror from two slightly curved plates, of which the edges facing one another interflt in a zigzag manner, with a view to avoiding the fleld distortion which occurs at these edges at high frequencies.

The present invention has for its object to obviate as much as possible the aforesaid disadvantages in a simple manner.

In an electric discharge tube according to the invention the stream of electrons is formed into 9 Claims. (Cl. 313-30) a beam which is directed on to an electron mirror which serves at the same time as a deflection member and consists of at least two electrodes between which a material is sandwiched having a dielectric constant which is different from that of the ambient space of the electrodes, in which material the electrostatic displacement takes place for at least 25%. Owing to the dielectric.

the reflecting fleld formed by the voltages fed to the electrodes of the electron mirror is shaped into a form which is different from that which would be produced in the absence of the dielectric.

The construction accozding to the invention permits the deflecting reflective field to be given substantially any desired form, since the dielectric may be shaped in such manner as to satisfy any desired form of the fleld. This desired form can be calculated beforehand and on the basis of these calculations the shape of the dielectric can be determined.

For the aforesaid construction the dielectric will be given such a shape that marginal distortion is substantially avoided. If, however. it is desired to influence the electron beam by means of the fleld in a different manner, for example, to concentrate it, this may be effected by giving the dielectric a diiferent shape. In this case, marginal distortion can be avoided at the same time.

As an alternative, the electric field for the mirror electrodes may be varied by using a dielectric which is completely evenly distributed between the electrodes, but wherein the dielectric constant is not the same throughout the material. This may be achieved by a definite choice of the composition of the dielectric.

In a particularly simple construction of the discharge tube according to the invention the electron mirror consists of two parallel plates which extend approximately in the same direction as the stream of electrons emitted by the cathode. Between these plates is provided a block of insulating material having a deflnite shape and/or a definite composition. This block of insulating material may at the same time serve as a fixture for the electrodes.

In order to render the discharge tube according to the invention also suitable for low frequencies, the electrodes forming the electron mirror may be interconnected by a high-ohmic resistance layer which is provided at the side of the dielectric facing the cathode. Owing to this construction the tube is suitable both for high and low frequencies.

For the dielectric use is preferably made of a substance having a dielectric constant exceeding 4. Good results are obtained, for example, with titaniumdioxide or porcelain.

In order that the invention may be more clearly understood and readily carried into effect, it will now be described more fully with reference to the accompanying drawing, given by way tem shown in Fig. 2.

Fig. illustrates the potential distribution of the electrode system shown in Fig. 4.

Fig. 6 shows a further embodiment which, according to the invention, may be substituted for the electrode system shown in Fig. 2. a

Fig. 7 illustrates the potential distribution of the electrode system shown in Fig. 6 and Fig. 8 show a third embodiment of the invention, which may be used instead of the electrode system shown in Fig. 2.

Referring to Fig. l the reference numeral I designates the wall of the discharge tube which is sealed at the lower side to a base plate 2 comprising a number of lead-out members 3 and a location member 4. The electrodes of the electrode. system, which is shown diagrammatically, are secured to .the said members 3 within the tube. The electrode system comprises a cathode 5 having a filament 6, a diaphragm I and an acceleration anode 8. The system 5 to 8 permits of producing an electron beam which is indicated diagrammatically by-a broken line 9. This beam 9 is directed through the electron mirror system more determined by the electrostatic displace-.

ment between the electrodes l2 and I3 than by the galvanic current in the resistance layer on the mica connecting plate It. It is obvious that a field which varies in such a manner is not suitable for even deflection of the beam.

Fig. 4 shows an electron mirror system which, according to the invention, is substituted for the system shown in Figures 1 and 2, which does not at the top of the tube to the anodes I0 and II.

The electron mirror system at the top of the tube, which is shown on an enlarged scale in Fig. 2, comprises two slightly curved electrodes i2 and i3 which are interconnected by a mica plate H in the usual manner.. The lead-out members for the electrodes i2 and i3 terminate in connecting caps l5 and E6 to which is connected a coil ll wherein an alternating voltage can be induced by means of a second coil i8,'so that opposite deflection voltages are applied to electrodes i2 and i3. Coil H has a mid-point tapping to which is applied, through point it, a voltage which is negative relatively to cathode 5. Owing to this negative voltage set up at the electron mirror system 82 and is, the beam 9 is deflected, as shown, anddirected on to the anodes i6 and ii. As stated the electron mirror system is of a conventional construction. On the side facing the cathode the mica plate id is coated with a high ohmic resistance layer which interconnects the two electrodes i2 and is. This layer is formed, for example, by a coating of aquadag.

Fig. 3 shows the distribution of potential produced between the electrodes 52 and i3 when a high-frequency alternating voltage of a frequency exceeding, for example, 10 c./s. is supplied via coils i 8 and H. As shown in this figure this potential does not vary according to a straight line but according to a curved line which exhibits the greatest curvature at the electrodes. This curvature is due to the fact that the field is operate satisfactorily. The mirror system'shown in Figure 4 comprises two slightly curved electrodes 20 and 2! which are interconnected by a block of insulating material 22. From the figure it appears that midway between the electrodes this block of insulating material is thinner than at the sides. Since the insulating material 22 is so thick that the electrostatic displacement takes place to at least 25% therein this particular form of the insulating material permits or ensuring a field distribution as shown in Figure 5, it the deflection voltages are supplied through the supply conductors 23 and 24 in a manner similar to that shown in Figure 1.

Fig. 6 shows an entirely diflerent construction of an electron-mirror deflection system which may be used in a tube according to the invention. It comprises electrodes 25- and 26 which in this present case are not arranged in a plane which extends substantially at right angles to the directions of the beam, but in two parallel planes which extend in substantially the same direction as the electron beam designated 21. Between the electrodes 25 and 26 is a block of insulating material 28 the dielectric constant of which exceeds that of the ambient space of the electrode system. Owing to the particular shape of the insulating material 29 a distribution 01' potential as shown in Fig. 7 is obtained in front of the electron mirror.

Fig. 8 shows afurther construction of an electrode system which may be used in a discharge tube according to the invention. In this figure the reference numerals 29 and 30 designate electrodes which similarly to those of the construction shown in Fig. 6, extend substantially parallel to the electron beam. The direction of this electron beam is designated 3l. The insulating material 32 engages completely and evenly the space between the electrodes 29 and 30. However, the dielectric constant of the material at the side of the electrode 29 is smaller than at the side of the electrode 30, which is shown by the varying cross-hatching. It will thus be possible to ensure a distribution of potential substantially corresponding to that shown in Fig. 7. Furthermore Figure 8 shows that on the side of the electron mirror facing the cathode the insulating material is coated with a high-ohmic resistance layer 33. Owing 'to this resistance layer, the tube comprising this electron mirror system is also suitable for lower frequencies. In th s event the resistance layer 33 is connected to the two electrodes 29 and 30. However, this is not necessary, since it may be alternatively connected only to one of the electrodes. In this case the operament comprising two electrode members spacedly positioned adjacent to each other and a mass of dielectric material in the space between said electrode members, said dielectric material having a dielectric constant differing from the dielectric constant of the space within said envelope, said displacement element having a capacitance per unit length varying over the length of said mass of dielectric material and said mass of dielectric material capable of having an electrostatic displacement of at least 25%.

2. An electric discharge tube comprising an envelop and within said envelope a source of an electron beam, a collector electrode within 'said envelope adjacent said beam source and spaced therefrom, and an electrostatic displacement element interposed between said beam source and said collector electrode and arranged in the path of said beam to repel said beam and deflect the same towards said collector electrode, said element comprising two electrode members spacedly positioned adjacent to each other and a mass of dielectric material in the space between said electrode members, said dielectric material having a dielectric constant differing from the dielectric constant of the space within said envelope, said displacement element having a capacitance per unit length varying over the length of said mass of dielectric material and said mass of dielectric material capable of having an electrostatic displacement of at least 25%.

3. An electric discharge tube comprising an envelope and within said envelope a source of an electron beam, a collector electrode within said envelope and spaced from said beam source, an electrostatic displacement element spaced from said beam source and arrangedin the path of said beam to repel said beam and deflect the same towards said collector electrode, said element comprising two electrode members spacedly positioned adjacent to each other and a mass of dielectric material in the space between said electrode members, said dielectric material having a dielectric constant differing from the dielectric constant of the space within said envelope, said displacement element having a capacitance per unit length varying over the length of said mass of dielectric material and said mass of dielectric material capable of having an electrostatic displacement of at least 25%, and a high-ohmic resistance layer facing said source of said electron beam and positioned on said electrostatic displacement element.

4. An electric discharge tube comprising an envelope and within said envelope a source of an electron beam, a collector electrode within said envelope and spaced from said beam source, and an electrostatic displacement element spaced from said beam source and arranged in the path of said beam to repel said beam and deflect the same towards said collector electrode, said element comprising two electrode members spacedly positioned adjacent to each other and a mass oi. dielectric material in the space between said electrode members, said dielectric material having a dielectric constant diiiering from the dielectric constant of the space within said envelope, said displacement element having a thickness per unit length varying substantially continuously over the greater portion of the length of said mass of dielectric material and said mass of dielectric material capable of having an electrostatic displacement of at least 25%.

5. An electric discharge tube comprising an envelope and within said envelope at source of an electron beam, a collector electrode within said envelope and spaced from said beam source, and an electrostatic displacement element spaced from said beam source and arranged in the path of said beam to repel said beam and deflect the same towards said collector electrode, said element comprising two electrode members spacedly positioned adjacent to each other and a mass of dielectric material in the space between said electrode members, said dielectric material having a dielectric constant diflering from the dielectric constant of the space within said envelope, said dielectric material of said displacement element having a dielectric constant varying-incrementally over the length of said mass oi! dielectric material and said mass of dielectric material capable of having an electrostatic displacement of at least 25%.

6. An electric discharge tube comprising an envelope and within said envelope a source of an electron beam having an initial direction, a, collector electrode within said envelope spaced from said beam source andout of the initial path of said beam, and an electrostatic displacement element spaced from said beam source and arranged in the initial path of said beam to repel said beam and deflect the same towards said collector electrode, said element comprising two electrode members spacedly positioned adjacent to each other and a mass of dielectric material in the space between said electrode members, said dielectric material having a dielectric constant greater than the dielectric constant of the space within said envelope, said displacement element having the dielectric material thereof proportioned to a greater thickness at the edges than in the center of the length of said mass of dielectric material and said'mass of dielectric material capable of having an electrostatic displacement of at least 25%.

'7. An electric discharge tube comprising an envelope and within said envelope a source of an electron beam having an initial direction, a collector electrode within said envelope and spaced from said beam source, and an electrostatic displacement element spaced from said beam source and arranged in the path of said beam to repel said beam and deflect the same towards said collector electrode, said element comprising .two electrode members spacedly positioned adjacent to each other substantially parallel to the said initial path of said electron beam and a mass of dielectric material in the space between said electrode members, said dielectric material having a dielectric constant differing from the dielectric constant of the space within said envelope, said displacement element having a thickness per unit length gradually increasing over the major portion of the length of said mass of dielectric material from one to the other of said electrodes and said mass of dielectric material capable of having an electrostatic displacement of at least 25%.

8. An electric discharge tube comprising an envelope and within said envelope a source of an electron beam having an initial direction, a collector electrode within said envelope and spaced from said beam source, and an electrostatic displacement element spaced from said beam source and arranged in the initial path of said beam to repl said beam and deflect the same towards said collector electrode, said element comprising two electrode members spacedly positioned adjacent to each other substantially parallel to the said initial path of said electron beam and a mass 0! 7 dielectric material in the space between said electrode members, said dielectric material having a dielectric constant diflerins irom the dielectric constant at the space within said envelope, said dielectric material oi said displacement element having constituents oi diiierin: dielectric constants over the length of said mass oi dielectric material and said mass oi dielectric material capable oi having an electrostatic displacement oi at least 25%.

9. An electric discharge tube comprising. an envelope and within said envelope 9. source oi an electron beam having an initial direction, a collector electrode within said envelope and spaced irom said'beam source, an electrostatic displacement element spaced irom said beam source and arranged in the initial path oi said beam to repel said beamand deflect the same towards said colleetor electrode, said element comprising two electrode members spacedly positioned adjacent to each other substantially parallel to the said initial path oi said electron beam and a mass of dielectric material in the space between said electrode members, said dielectric material having a dielectric constant differing irom the dielectric constant oi the space within said envelope, said dielectric material of said displacement element having constituents oi diiierins dielectric con-. stants over the length oi said mass oi dielectric material and said mass oi dielectric material capable oi having an electrostatic displacement of at least 25%, and a high ohmic resistance layer iacing said source oi said electron beam and positioned on said electrostatic displacement element.

ADRIANUS JOHANNES WILHELMUS .MARIE VANOVERBEEK.

REFERENCES CITED The icliowinz reierences are of record in the file of this patent:

UNITED STATES PATENTS Australia Oct. 22, 1942 

